The invention relates to a hydraulic dualcircuit tandem main brake cylinder for vehicle brake systems. The system has at least one brake piston for one closed brake circuit. A control valve device is actuatable via a pedal-actuated control tappet and includes a travel simulator spring and directs a control pressure into a pressure chamber adjoining at least one piston. An auxiliary piston member adjoins the pressure chamber, which member comprises an auxiliary piston and a tappet passing therethrough which is actuated by the pedal. A progressive spring is fastened in place between one side of the auxiliary piston remote from the pressure chamber and the tappet passing through this auxiliary piston. Such an apparatus is disclosed in German Patent Application P 32 10 735.8.
The essence of the above listed patent is that the pressure directed into the pressure chamber has a limited feedback effect as a reactionary force on the pedal via the brake valve, but a very much greater effect on the pedal via the tappet passing through the auxiliary piston.
In the structure of the above listed patent, a disadvantageous feature is related to the simulator spring, which upon a quick actuation of the brake pedal, a phase displacement takes place between the pedal force exerted and the feedback to the pedal of the brake pressure effected.